Bipolar components have two emitters doped complementarily to one another and at least one base zone, which is more lightly doped than the emitters and is arranged between the emitters. When the component is in the on state, charge carriers are emitted into the base zone by the emitters, as a result of which a charge carrier plasma is formed in the base zone. When the component is turned off, the charge carriers that form the charge carrier plasma have to be removed from the base zone, which leads to turn-off losses.
IGBTs usually have an n-type source zone, which, by means of an inversion channel controlled via a gate electrode, serves as an electron source and can therefore be considered analogous to an n-type emitter in its function. The n-type source zone is separated from an n-type base zone by a p-type base zone or p-type body zone. An IGBT additionally comprises a p-type emitter, which is arranged on a side of the n-type base remote from the p-type body zone. In the case of an IGBT, the charge carrier plasma density in the n-type base is determined by the efficiency of the p-type emitter, in particular. In this case, a high emitter efficiency means a low forward voltage when the component is in the on state, but also leads to high turn-off losses upon turn-off. This is due to the fact that the charge carriers stored in the n-type base in the on state have to flow, upon turn-off, through the space charge zone established in the off state, which leads to turn-off losses.
In order to reduce turn-off losses, in the case of an IGBT, in addition to a gate electrode controlling a channel in the p-type base, a further control electrode can be provided, which serves to short-circuit or bridge the p-type emitter shortly before the component is actually turned off. The p-type emitter thus becomes inactive, as a result of which the density of the charge carrier plasma is reduced before the component is actually turned off.
When the component is in the off state, the n-type emitter or the n-type source and the p-type emitter are at different electrical potentials. These electrical potentials can differ by up to a few 100 V or up to a few kV depending on the dielectric strength of the component. Accordingly, in the case of conventional IGBTs having two control structures, two separate drive circuits are required. The first drive circuit serves to generate a drive voltage for the gate electrode, the drive voltage being relative to the potential of the n-type emitter or of the n-type source. The second drive circuit serves to generate a drive voltage for the additional control electrode, the drive voltage being relative to the electrical potential of the p-type emitter. These two drive circuits have to be electrically insulated from one another in a suitable manner in order to avoid voltage flashovers.